This invention relates to microorganisms that have been improved by genetically engineering an ability to utilize a given substrate, thereby possessing a competitive advantage in their ability to colonize a given localized environment such as a rhizosphere.
The beneficial effects of bacteria that naturally colonize the environment near plant roots (the rhizosphere) has been known for some time. See, for example, Weller, in: Ann. Rev. Phyopathol. 26:379-407 (1988), which provides a comprehensive review. One way to encourage preferential colonization of a desired species of microorganism is to introduce a microorganism that has an ability to produce a anti-microbial substance such as is described in copending U.S. patent application Ser. No. 579,457, filed Sep. 7, 1990. Another way to encourage preferential colonization of a desired species of microorganism would be to engineer the desired species to confer a superior ability to utilize a limited substrate occurring in the localized environment in which it occurs. In this way, the colonization of the desired species is enhanced and colonization of undesired inferior substrate utilizing species is controlled.
Chemicals found in the rhizosphere called calystegins have been described as being used by certain microorganisms as a sole carbon source, with the ability to utilize the calystegins being attributable to a segment of DNA [Tepfer et al., Molecular Genetics of Plant/Microbe Interactions, Palacios and Verma, editors, APS Press, (1988) PP. 139-144; Tepfer et al., J. Bacteriol., 170:1153-1161 (1988); Tepfer et al., "Ri T-DNA from Agrobacterium rhizogenes: a source of genes having applications in rhizophere biology and plant development, ecology and evolution" in Plant-Microbe Interactions, vol. 3 (editors Kosuge and Nester), McGraw-Hill Publishing Co., (1989) pp 294-343; Tepfer et al., European Patent Application 203863, published Dec. 3, 1986].